This invention relates generally to fire and explosion detection systems and more particularly to a discriminating system for the prevention of false alarms.
Fire detection systems which respond to the presence of either a flame or an explosion for generating an output control signal used for activation of a fire suppressant are generally known. Typical of such systems is a sensor for determining the existence of radiation at a wavelength corresponding to CO.sub.2 emission which is characteristically associated with a hydrocarbon fire.
In military applications it is desirable to discriminate against a hydrocarbon fire which can be produced by, for example, the explosion of a fuel tank in vehicles such as armored personnel carriers or tanks and high energy "High Energy Anti-Tank" (HEAT) rounds. HEAT rounds cause momentary high-energy radiation levels and high temperatures (&gt; 3000.degree. K. and often &gt; 5000.degree. K.) due not only to the ammunition round itself but due to a secondary reaction with the vehicle's armor theorized as a pyrophoric reaction. HEAT rounds may or may not, however, set off a hydrocarbon fire. Thus, it is desired to prevent activation of a fire suppressant where a HEAT round enters a vehicle but does not explode the fuel tank and does not cause a fire.
U.S. Pat. No. 3,825,754 issued July 23, 1974 to Cinzori et al. discloses a detecting system which includes sensing means for specifically detecting a HEAT round and responding to the detection of such a round to deactivate the hydrocarbon fire detecting means of the system for a period of time. If after the delay period a hydrocarbon fire is detected, the fire suppressant will be activated. A significant disadvantage with prior art of this type is that during the delay period an explosive hydrocarbon fire can be well underway before the system detects it and actuates the suppressant. Thus there is a need for an improved discriminating fire detecting system which although providing the desired discrimination between HEAT rounds which do not cause a resultant explosive hydrocarbon fire and ones that do is not undesirably disabled for a delay period in which an explosive hydrocarbon fire can get out of control before the suppressant is activated.